Gliederung

Objective: Decompressive craniectomy is a common treatment for otherwise fatal progressive brain swelling in stroke and traumatic brain injury. However, the optimal point in time for re-implantation of the bone flap is still a matter of debate. Most of the surviving patients undergo cranioplasty after a period of several months, but cosmetic arguments and protective factors favour an early cranioplasty. So far, little attention has been paid to the biomechanical aspects of decompressive craniectomy. The tissue deformation occurring in these patients is hard to quantify, and it is even more complicated to describe the tissue movements occurring during postural changes.

Methods: Twenty-five consecutive patients (median age 51 years; 9 female, 17 male) suffering from a large bone defect after craniectomy and scheduled for cranioplasty were examined in the supine position. The third ventricle's axial diameter was measured by transcranial ultrasound using a 5.0 MHz ultrasound probe. Subsequently, the patient was brought into a sitting position, either by modifying the bed position or by asking cooperative patients to sit. After 5 minutes, the measurement was repeated. This procedure was repeated for about 7 days after cranioplasty. Data of 12 healthy volunteers (median age 38 years; 6 female, 6 male) were compared.

Results: In the healthy volunteers, the third ventricle's axial diameter was enlarging after reaching the sitting position. The median diameter was 2.35mm in the supine position and 2.9mm in the sitting position (p>0,05). In most of the patients before cranioplasty, a decrease of the diameter after reaching the sitting position was observed. The median diameter was 8.6mm in the supine and 7.5mm in the sitting position. After cranioplasty, most of the ventricles dilated in orthostasis. The median diameter was 7.1mm in the supine and 7.6mm in the sitting position.

Conclusions: These data demonstrate that ultrasound is capable of examining pathophysiological changes of brain compliance in patients after craniectomy in vivo. Our observation of atypical brain movements due to a change in the body position provides a novel argument for earlier cranioplasty.